Wnt signaling pathways are critically involved in cell fate determination, and aberrations in Wnt signaling have been directly implicated in human cancer. Our research within this project has focused on elucidating mechanisms that regulate canonical signaling through Wnt co-receptors, LRP5/6 and Fz, and the actions of naturally occurring Wnt antagonists, FRP1 and DKK1. We have also applied knowledge gained to the discovery of Wnt autocrine signaling in some human tumor cells. We plan to continue investigations of receptor activation mechanisms and novel aspects of intracellular signaling that could provide insights into other aberrations in human tumor cells involving b-catenin dependent TCP signaling. Aim 1 of this proposal is directed toward further elucidation of Wnt ligand/receptor interactions and receptor genetic lesions that can constitutively activate Wnt receptors as well as interacting cellular proteins, which modulate receptor functions. Aim 2 focuses on investigating the functions of Wnt signaling in normal postnatal tissues and in tissue culture cells as well as the effects on proliferation and differentiation caused by inhibition of this pathway in human tumor cells with constitutive Wnt signaling upregulation. In Aim 3, we plan to further characterize mechanisms of autocrine Wnt signaling in human tumor cells as well as other explore other activation mechanisms focusing initially on alterations afflicting Wnt receptors or receptor interacting proteins. Based on our preliminary evidence, we will also attempt to identify coactivator(s) for a novel b-catenin independent TCF1/LEF1 signaling pathway. In summary, investigations within this project are directed toward establishing new insights into Wnt transforming mechanisms that may eventually lead to novel interventions with this pathway in human cancers.